Cytoplasmic and nuclear vasopressin RNA in hypothalamic and extrahypothalamic neurons of the Brattleboro rat: An in situ hybridization study

In situ hybridization was performed in Long-Evans (LE) and heterozygous (HET) and homozygous (HOM) Brattleboro rats using a 48-base oligonucleotide complementary to the last 16 amino acids of the vasopressin messenger RNA (VP mRNA). The number of cells expressing the VP mRNA in the supraoptic (SON) and paraventicular (PVN) nuclei was not significantly different between LE, HET, and HOM rats; however, the relative amount of mutant VP mRNA expressed in neurons of the PVN and SON of the HOM rat was significantly lower than that in the other two genotypes. In contrast, the suprachiasmatic nucleus (SCN), the bed nucleus of the stria terminalis (BNST), and the medial amygdala (MA) of the HOM rat showed a significant reduction in both the number of neurons and the level of mutant VP mRNA expression per cell compared to those in either the LE or the HET rat. To determine whether the reduced level of mutant VP mRNA in the HOM rat was due to decreased transcription, in situ hybridization to detect the VP primary transcript was performed. The number of neurons and the amount of nuclear VP RNA expressed per cell for the PVN, SCN, BNST, and MA in the HET and HOM rats were not significantly different from those in the LE rat. However, in the SON, the HOM rat exhibited a significant increase (P < 0.10) in the amount of nuclear VP RNA expressed per cell compared to the LE and HET rats, but the number of positively labeled cells was not significantly different. Therefore, these data suggest that the mutant gene in the HOM rat is transcribed at rates comparable to those in the LE and HET rats, while cytoplasmic mutant VP mRNA is significantly reduced in all nuclei of the HOM rat. The reduced cytoplasmic VP mRNA in the HOM rat may be attributed to instability (degradation) of the mutant message.